1. Field of the Invention
This invention relates generally to automotive vehicle dynamics, and more particularly to improvements in processing data from certain on-board sensors, including a steering wheel relative position sensor and a yaw rate sensor, to derive information useful for control of certain aspects of vehicle dynamics through one or more control systems.
2. Background Information
Certain motion sensors, such as steering wheel position sensors and yaw rate sensors for example, provide useful inputs to an automotive vehicle control system. Such a control system utilizes a microprocessor that processes data, including input signal measurements received from such sensors, to cause adjustments in and/or actuations of control devices. The responses of such sensors can be sufficiently fast in relation to vehicle motion that their signal measurements can very closely track changing values of the respective measured parameters in real time. Accordingly, a microprocessor-based control system which receives such signal measurements as inputs can quickly process them to perform desired control action, such as performing a control function that strives to correct for rapidly changing vehicle dynamics via an appropriate system of the vehicle.
Certain automotive vehicle control systems, such as a stability assist control system, require an input that identifies the correct direction of actual vehicle travel with a very high degree confidence so that proper control functions can be executed, plausibility checks for confirming integrity of the system and sensors can be carried out, and offsets and calibrations of sensors can be established. In common driving situations, the direction of vehicle travel can be determined from the particular drive gear selected. Certain situations where this is not true can occasionally arise. Examples of those situations include vehicles spins, neutral gear selection, a vehicle rolling down a grade, a vehicle lacking sufficient traction to climb a grade and sliding down in a direction opposite the selected gear, and a failure that causes the gear selection information to be incorrect or unavailable.
In general, a dynamic relationship exists between the steering wheel angle and the vehicle yaw rate. For a steady state operating condition at a given speed and a given absolute steering wheel angle, the yaw rate has approximately the same magnitude whether the vehicle is traveling forward or backward. The sign of the yaw rate changes (+/-) when the direction is changed, but the magnitude does not change significantly. This sign reversal is also true during dynamic vehicle maneuvers, but during such maneuvers, the difference in magnitude is greater than that for the steady state condition because the vehicle is steered by turning the leading wheels, and not the trailing ones. This relationship between the absolute steering wheel angle and vehicle yaw rate can be used to determine travel direction of the vehicle.
A sensor which measures absolute steering wheel angle provides a signal of the absolute position of the steering wheel angle relative to a known reference point and at present is significantly more expensive than one which measures relative steering wheel angle. A sensor which measures relative steering wheel angle provides a signal only of relative change in the steering wheel angle. For example, when a relative steering wheel angle sensor is off and the steering wheel is turned, the sensor does not detect the turning. An absolute steering wheel angle sensor will be able to distinguish new steering wheel angle positions regardless of whether the sensor has been off during the period of time in which the change in steering wheel angle was made.
It is believed that an ability to correctly identify the direction of vehicle travel without relying exclusively on gear selection and without using an absolute steering wheel angle sensor would be advantageous.